1. Field of the Invention
The present invention relates to a slide driving method for a link type transfer press which is used for automatically and continuously carrying out a process beginning with insertion of a workpiece and ending with completion of processing of the workpiece within a single press, and also relates to a link type transfer machine.
2. Description of Related Art
Among several press machines, there has been well-known a transfer press which can consistently carry out a process for products, which requires several process steps beginning with insertion of a workpiece and ending with completion of processing of the workpiece in a single press.
In a transfer press, blanks (workpieces) separated from one another are transferred successively into dies in a next process station by means of a pair of feed bars constituting a feeder, and fingers attached thereto, and a slide to which the dies are attached is moved up and down in association with this transfer operation so as to carry out pressing operation.
In the so-called link type transfer press, the elevation of the slide is carried out with the use of a link mechanism.
In a conventional transfer press, the slide is moved down from the top dead center in a fast forward mode until an upper die abuts against a workpiece, and after molding of the workpiece, the slide is moved up to the top dead center in a fast forward mode.
In the above-mentioned conventional link type transfer machine suffers from hindrances to the enhancement of productivity, one of which is a limitation to the feed speed of the feeder, which disable the stroke frequency per minute (SPM) from being increased. In other words, if the time required for one cycle is shortened, a required feed time of the feeder cannot be ensured.
That is, as shown in FIG. 8, the conventional slide motion curve is such that the slide descends from the top dead center A in a fast forward mode, and after completion of press molding at the bottom dead center B, the slider rapidly ascends therefrom to the top dead center A in a fast forward mode. During one cycle of the slide from the top dead center to the dead center, and then to the top dead center, a range (time) in which the feeder can be transferred without interference with the slide is exhibited by the time (T1+T1) from the starting point O of the cycle to a position C to which the slider descends from the top dead center A by a predetermined distance H on both sides of the starting point O.
Meanwhile, the transfer speed of the feeder is determined by a relationship of inertial moment and the like, and as a result, a required time t1 for the cycle from the top dead center A to the top dead center A is inevitably determined.
It is noted, referring to FIG. 8, that the required time for one cycle with respect to the starting point O is taken along the abscissa, and the slide stroke is taken along the ordinate. Although the angle is usually taken along the abscissa, this exhibition can hardly be understood, and accordingly, the cycle time is taken therealong for the sake of convenience in understanding.
In the above-mentioned slide motion, it may be considered that a time t2 required for one cycle is simply shortened to a value smaller than the above-mentioned time ti, as exhibited by a phantom line (two-dot broken line) in FIG. 8, and as a result, the time required for the entire process is shortened in order to enhance the productivity.
However, in the conventional slide motion, should the time required for one cycle be simply shortened from the time t1 to the time t2, would cause such a problem that a possible transfer range of the feeder in the slide motion, that is, the time T2+T2 which corresponds to a range from the starting point O of the cycle to the position C to which the slide descends from the top dead center A by the predetermined distance H, become shorter than the above-mentioned time T1+T1.
Meanwhile, the transfer time of the feeder requires a certain predetermined time in view of the inertial moment of the feeder and the like, and accordingly, in the normal slide motion, the transfer motion of the feeder is designed in accordance with the critical value. Thus, if the transfer time of the feeder is shortened, the transfer of the feeder becomes insufficient, and accordingly, the feeder interferes with the slide so as to raise such a problem that a predetermined pressing process can not be made.
An object of the present invention is to provide a slide driving method in a link type transfer press and a link type transfer press, which can enhance the SPM of a slide while the transfer time of the feeder is ensured so as to enhance the productivity.
To the end, according to the present invention, there is provided a slide driving method for a link type transfer press which is always coupled to a drive source so as to move a slide up and down through the intermediary of a slide drive mechanism, characterized in that the slide is driven by continuously dwelling the slide in the vicinity of the dead center thereof without stopping a press.
In this arrangement of the present invention, since the slider dwells in the vicinity of the top dead center thereof for a predetermined time, the motion index angle (transfer time) of the feeder which is dominant in the entire cycle can be taken by a large degree so as to enable the transfer time t2 of the feeder to be substantially longer even thought a time required for one cycle of the slide is shortened. As a result, the SMP of the slider can be enhanced while the transfer time of the feeder can be ensured so as to shorten the entire press time, thereby it is possible to aim at enhancing the productivity.
In the present invention, xe2x80x9cdwellxe2x80x9d means that the slider stops or stays in a constant condition. More specifically, the slide substantially uniformly holds its height for a predetermined time in the vicinity of the top dead center even though the press is operated. As to the dwell condition, although there may be considered along the top dead center a wavy condition, a horizontal condition, a certain wavy swelling condition or the like, there may be included a right shoulder descent condition since it is sufficient to stop or stay in the vicinity of the top dead center.
The characteristic feature of the present invention is to provide the link type transfer press with a dwell mechanism for causing the slide to continuously dwell in the vicinity of the top dead center without stopping the press.
As to the dwell generating mechanism, an existing link mechanism, a link mechanism using an eccentric drum or the like may be used, and further, a cam mechanism having a profile in accordance with a dwell may also be used. However, a link mechanism is preferably used since it is structurally simple and can be simply manufacture.
In this arrangement, since the slide can continuously dwell in the vicinity of the top dead center by means of the dwell generating mechanism, the moving time of the feeder can be made to be longer even though the time required for one cycle is shortened, and accordingly, the feeder can be fed without interfering with the slider during this period. As a result, the SMP of the slide can be enhanced so as to shorten the press time in its entirety. Thereby, it is possible to enhance the productivity.